This invention relates to railway communications systems, and, in particular, to “off-board” communications between a railbound vehicle and a central station or control center of a railroad.
As used herein, a railbound vehicle means any railroad asset or vehicle which may require or benefit from the transmission or reception of data, including a locomotive, a maintenance-of-way (MOW) vehicle, or other vehicle. For convenience, this invention will be discussed principally in terms of a locomotive.
As used herein, “off-board” communications refer to communications between a locomotive, railcar, or other railroad “asset” which is in service (i.e., traveling over a line of road of a rail system), and a control center. The communications are typically two-way wireless communications in which a radio, for example, transmits signals to, and/or receives signals from the control center. The communications need to be timely and reliably sent and received, transmitted in a cost-effective manner, and have a high information “throughput”. Throughput refers to the amount of information (data) transmitted during a defined time interval; for example, bits per second or bps. Since the control center is usually some distance away from the train, off-board communications are sent via satellite, a cellular communications system, or other radio based infrastructure.
Since the communication are two way communications, this means data is both sent from and to the track asset. Information communicated from the locomotive to the control center will sometimes include “health and status” data relating to such things as train speed, operating temperature of the locomotive's engine(s), fuel consumption, etc.; as well as the physical location of the train on the rail line. This latter is important because locomotives often get “misplaced”, especially when loaned to another rail carrier for use on the other carrier's track. Accordingly, information giving the precise location of a train or locomotive aids the railway in controlling its operations and its assets. At other times, the information will relate to “work orders” which describe activities for crews to accomplish by specific times or at specific locations.
Information communicated to the locomotive from a control center(s) could include safety information, such as track warrants or other locomotive proximity data; or, it could be other general purpose data, such as track database information. Safety information (sometimes referred to as “vital” information) needs to be communicated precisely and with a very low chance of data error.
It is important to note that off-board communications are expected to increase dramatically in the near future. Locomotives, maintenance-of-way vehicles, and railcars have an increasing number of microprocessors and sensors installed throughout. Railroads are now recognizing the advantage of better managing their information to improve their tactical and strategic operations. For the purposes of this discussion, a locomotive transmitting data to its associated control center(s) will be used as the descriptive example.
A typical locomotive communications system includes a central processing unit (CPU) which collects data to be transmitted to the control center from various sensors (and other subsystems) located onboard the locomotive and throughout the train, and arranges this data in an appropriate format for transmission. The CPU routes the formatted data to a radio transmitter and associated antenna for transmission. This usually occurs at regular, established intervals. For instance, the locomotive may be required to transmit every half-hour, on the hour and half-hour. When it is time to transmit, the on-board transmission system first tries to establish a communication's path from the train to the control center. For a radio transmission, this may involve a two-way “handshake” protocol to locate a signal tower. If a convenient signal tower is found, the locomotive's transmission system directs the data transmission through the communication's path now provided by the tower to the control center. Unfortunately, signal towers are not always conveniently located near railroad tracks, whether in parts of the United States, as well as in foreign countries. If a signal tower cannot be found, an attempt may be made to establish an alternate communication's path using a satellite or cellular system, for example. If, however, such alternate path cannot be established, a transmission may not be attempted. Rather, the system will wait until its next scheduled time and attempt the transmission again. It will be understood that the locomotive may have traveled some distance during this interval. Also, since time will have elapsed, the data which previously would have been sent will not now be current. Accordingly, it is important that when off-board communications take place, that they be reliable and fast so the information is timely transmitted to the control center and important information and data is not missed.
Wireless communications are not perfect. Besides a communications path not always being the best, other factors such as terrain and atmospheric conditions will affect the quality of the communications so that, on occasion, only a weak signal or a broken signal reaches the control center. In such circumstances, necessary information may either not be received at all; or if received, will be incomplete.
Finally, there is a cost factor associated with off-board railway communications. Railway communications not only avail themselves of signal towers which are usually not owned by the railway, but also satellites or cellular communications systems that are owned by telecommunications companies and not the railroad. Since the railroad leases these communications facilities for their data transmissions from these companies; to be cost effective, the transmission of off-board communications needs to be as efficient and complete as possible so data being downloaded is complete and the data does not have to be resent.